Stent designs for use in peripheral vessels

ABSTRACT

System including a delivery catheter and a stent disposed at a distal end of the delivery catheter. The stent includes a plurality of radially expandable rings disposed adjacent to one another to define a tubular member having a proximal end portion, and a distal end portion, and a middle portion, each of the radially expandable rings including a plurality of strut members. The middle portion of the tubular member include a plurality of interconnection members extending between longitudinally adjacent expandable rings, the number of the plurality of the interconnection members being greater than that of the end portion of the tubular member. The stent also includes a transition section between the end portion and the middle portion, the transition section including at least one open cell and at least one closed cell. The stent can be self-expandable or balloon expandable.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/844,235, filed Aug. 23, 2007, now U.S. Pat. No. 8,252,041 whichclaims the benefit of U.S. provisional application Ser. No. 60/823,352filed Aug. 23, 2006, the disclose of each of which is incorporated byreference in its entirety herein.

FIELD OF THE INVENTION

The present invention relates to expandable endoprosthesis devices,generally called stents, which are adapted to be implanted into apatient's body lumen, such as a blood vessel, to maintain the patencythereof. Stents are particularly useful in the treatment and repair ofblood vessels after a stenosis has been compressed by percutaneoustransluminal coronary angioplasty (PTCA), percutaneous transluminalangioplasty (PTA), or removed by atherectomy or other means, to helpimprove the results of the procedure and reduce the possibility ofrestenosis.

BACKGROUND OF THE INVENTION

Stents, grafts and a variety of other endoprosthesis are well known andused in interventional procedures, such as for treating aneurysms, forlining or repairing vessel walls, for Stents are generallycylindrically-shaped devices which function to hold open and sometimesexpand a segment of a blood vessel or other arterial lumen, such ascoronary artery. Stents are usually delivered in a compressed conditionto the target site and then deployed at that location into an expandedcondition to support the vessel and help maintain it in an openposition. They are particularly suitable for use to support and holdback a dissected arterial lining which can occlude the fluid passagewaythere through.

A variety of devices are known in the art for use as stents and haveincluded coiled wires in a variety of patterns that are expanded afterbeing placed intraluminally on a balloon catheter; helically woundcoiled springs manufactured from an expandable heat sensitive metal; andself-expanding stents inserted into a compressed state for deploymentinto a body lumen. One of the difficulties encountered in using priorart stents involve maintaining the radial rigidity needed to hold open abody lumen while at the same time maintaining the longitudinalflexibility of the stent to facilitate its delivery and accommodate theoften tortuous path of the body lumen.

Prior art stents typically fall into two general categories ofconstruction. The first type of stent is expandable upon application ofa controlled force, often through the inflation of the balloon portionof a dilatation catheter which, upon inflation of the balloon or otherexpansion means, expands the compressed stent to a larger diameter to beleft in place within the artery at the target site. The second type ofstent is a self-expanding stent formed from shape memory metals orsuper-elastic nickel-titanium (NiTi) alloys, which will automaticallyexpand from a compressed state when the stent is advanced out of thedistal end of the delivery catheter into the blood vessel. Such stentsmanufactured from expandable heat sensitive materials allow for phasetransformations of the material to occur, resulting in the expansion andcontraction of the stent.

Details of prior art expandable stents can be found in U.S. Pat. No.3,868,956 (Alfidi et al.); U.S. Pat. No. 4,512,1338 (Balko et al.); U.S.Pat. No. 4,553,545 (Maas, et al.); U.S. Pat. No. 4,733,665 (Palmaz);U.S. Pat. No. 4,762,128 (Rosenbluth); U.S. Pat. No. 4,800,882(Gianturco); U.S. Pat. No. 5,514,154 (Lau, et al.); U.S. Pat. No.5,421,955 (Lau et al.); U.S. Pat. No. 5,603,721 (Lau et al.); U.S. Pat.No. 4,655,772 (Wallstent); U.S. Pat. No. 4,739,762 (Palmaz); and U.S.Pat. No. 5,569,295 (Lam), which are hereby incorporated by reference intheir entirety.

Further details of prior art self-expanding stents can be found in U.S.Pat. No. 4,580,568 (Gianturco); U.S. Pat. No. 4,830,003 (Wolff, et al.);U.S. patent application Ser. No. 10/158,362 (Denison); and U.S. Pat.Nos. 6,537,311 and 6,814,749 (Cox, et al.), which are herebyincorporated by reference in their entirety.

Expandable stents are delivered to the target site by delivery systemswhich often use balloon catheters as the means for delivering andexpanding the stent in the target area. One such stent delivery systemis disclosed in U.S. Pat. No. 5,158,548 to Lau et al., which is herebyincorporated by reference in its entirety. Such a stent delivery systemhas an expandable stent in a contracted condition placed on anexpandable member, such as an inflatable balloon, disposed on the distalportion of an elongated catheter body. A guide wire extends through aninner lumen within the elongated catheter body and out its distal end. Atubular protective sheath is secured by its distal end to the portion ofthe guide wire which extends out of the distal end of the catheter bodyand fits over the stent mounted on the expandable member on the distalend of the catheter body.

Some prior art stent delivery systems for implanting self-expandingstents include an inner lumen upon which the compressed or collapsedstent is mounted and an outer restraining sheath which is initiallyplaced over the compressed stent prior to deployment. When the stent isto be deployed in the body vessel, the outer sheath is moved in relationto the inner lumen to “uncover” the compressed stent, allowing the stentto move to its expanded condition into the target area.

In many procedures which utilize stents to maintain the patency of thepatient's body lumen, the size of the body lumen can be quite smallwhich prevents the use of some commercial stents which have profileswhich are entirely too large to reach the small vessel. In particular,often in PTCA procedures, the stenosis is located in the very distalregions of the coronary arteries which often have small diameters. Manyof these distal lesions are located deep within the tortuous vasculatureof the patient which requires the stent to not only have a smallprofile, but also high flexibility to be advanced into these regions. Asa result, the stent must be sufficiently flexible along its longitudinalaxis, yet be configured to expand radially to provide sufficientstrength and stability to maintain the patency of the body lumen. Sincemany commercial stents lack both the low profile and extreme flexibilityneeded to reach such distal lesions, they are not available forutilization for such procedures.

What has been needed is a stent which has a low profile and a highdegree of flexibility so that it can be advanced through tortuouspassage ways of the anatomy and can be expanded within the body vesselto maintain the patency of the vessel. Additionally, the expanded stentmust have adequate structural strength (hoop strength) to hold the bodylumen open once expanded. Such a stent should also have sufficientradiopaque properties to permit it to be sufficiently visualized onexternal monitoring equipment, such as a fluoroscope, to allow thephysician to place the stent in the exact target location. The presentinvention satisfies these and other needs.

SUMMARY OF THE INVENTION

The present invention is directed to stents having low profiles whichcan be used in body vessels, such as the carotid arteries and otherperipheral arteries, along with the coronary arteries. The stents of thepresent invention are intended, but are not limited, to the effectivetreatment of diseased vessels having diameters from about 3.0 to 14.0millimeters.

The stents of the present invention can be formed from super elasticnickel titanium alloys, or other shape memory materials, which allow thestent to be self expandable. The expansion occurs when the stress ofcompression is removed. This allows the phase transformation frommartensite to austenite to occur, and as a result the stent expands. Thestents of the present invention can be processed to behavesuperelastically at body temperature. Alternatively, the stent designsof the present invention could be used in conjunction with balloonexpandable stents made from stainless steel or other conventional stentmaterials.

In all embodiments, the stents of the present invention have sufficientlongitudinal flexibility along their longitudinal axis to facilitatedelivery through tortuous body lumens, yet remain stable when expandedradially to maintain the patency of a body lumen, such as an artery orother vessel, when implanted therein. The present invention particularlyrelates to unique strut patterns which have a high degree oflongitudinal flexibility and conformability, while providing sufficientradial-expansibility and strength to hold open the body lumens. The highradial strength possessed by the stents of the present invention allowthem to be used in treating calcified lesions.

Generally, the greater the longitudinal flexibility of the stents, theeasier and the more safely they can be delivered to the implantationsite, particularly where the implantation site is on a curved section ofa body lumen, such as a coronary artery or peripheral blood vessel, andespecially in saphenous veins and larger vessels. The designs of thepresent invention have sufficient flexibility to conform to thepatient's vasculature, thus preventing vessel straightening by thestent. Moreover, the stents of the present invention are crush proof,making them particularly suitable for implantation in the carotidarteries.

Each of the different embodiments of stents of the present inventioninclude a plurality of adjacent cylindrical elements (often referred toas “rings”) which are generally expandable in the radial direction andarranged in alignment along a longitudinal stent axis. The cylindricalelements are formed in a variety of serpentine wave patterns transverseto the longitudinal axis and contain a plurality of alternating peaksand valleys. At least one interconnecting member (often referred to as a“spine”) extends between adjacent cylindrical elements and connects themto one another. These interconnecting members insure minimallongitudinal contraction during radial expansion of the stent in thebody vessel. The serpentine patterns have varying degrees of curvaturein the regions of peaks and valleys and are adapted so that radialexpansion of the cylindrical elements are generally uniform around theircircumferences during expansion of the stent from the collapsed positionto the expanded position.

The stents of the present invention also have strut patterns whichenhance the strength of the ends of the stent and the overallradiopacity of the stent, yet retain high longitudinal flexibility alongtheir longitudinal axis to facilitate delivery through tortuous bodylumens and remain stable when expanded radially to maintain the patencyof the body lumen. The present invention in particular relates to stentswith unique end portions having sufficient hoop strength to maintain aconstant inner diameter which prevents the stent from taking on a“cigar” shape when deployed in the body lumen. The end rings used withthe present invention are particularly useful on self-expanding stentswhich may otherwise have end rings that are more susceptible tocompressive forces.

The resulting stent structures are a series of radially expandablecylindrical elements that are spaced longitudinally close enough so thatsmall dissections in the wall of a body lumen may be pressed back intoposition against the luminal wall, but not so close as to compromise thelongitudinal flexibility of the stent both when negotiating through thebody lumens in their unexpanded state and when expanded into positionwithin the vessel. The design of the stents contribute to form smallgaps between struts to minimize tissue prolapse. Each of the individualcylindrical elements may rotate slightly relative to their adjacentcylindrical elements without significant deformation, cumulativelyproviding stents which are flexible along their length and about theirlongitudinal axis, but which still are very stable in their radialdirection in order to resist collapse after expansion.

In one embodiment of the present invention, each cylindrical element ofthe stent includes eight peak regions (often referred to as “crowns”)and eight valley regions which provide sufficient coverage of the vesselwhen placed in the expanded or deployed position. In this design, eachcylindrical element consisting of an alternating pattern of U-shapedportions and double-curved (W) portions connected both axially andcircumferentially to eight discontinuous interconnecting members orspines. For example, the U-shaped portion of the cylindrical element canbe connected to an adjacent cylindrical element via the interconnectingmembers. The same cylindrical element can be then connected to anothercylindrical element via the interconnecting members connected to thedouble-curved portions. The cylindrical element can be connected to anadjacent cylindrical element by four interconnecting members. Thisparticular alignment of interconnecting members provides adequateflexibility to the stent and also helps prevent foreshortening of thestent as it expands radially outward. The discontinuing pattern ofinterconnecting members results in a highly flexible stent that does notkink upon bending. Both the distal and proximal ends of this stentdesign can be entirely composed of “W” patterns which provide additionalstrength to the ends of the stent. The resulting stent produces an eightcrown, four-cell pattern which has sufficient coverage for vesselscaffolding while maintaining excellent flexibility to reach distallesions and possessing sufficient radial strength to hold the targetvessel open. An alternative pattern using six crowns and sixdiscontinuous interconnecting members also can be utilized and willexhibit these same physical properties.

The serpentine pattern of the individual cylindrical elements canoptionally be in phase with each other in order to reduce thecontraction of the stent along their length when expanded. In theseembodiments of the present invention, interconnecting members alignbehind each other to create a continuous “spine” which extends from oneend of the stent to the other. Two or three rows of continuous spinescan be used to connect adjacent cylindrical elements. This constructionalso helps prevent the stent from foreshortening when expanded.

A stent made in accordance with the present invention can be readilydelivered to the desired target location by mounting it on a stentdelivery catheter which includes a retractable sheath, or other means,to hold the stent in its collapsed position prior to deployment.

These and other features and advantages of the present invention willbecome more apparent from the following detailed description of theinvention, when taken in conjunction with the accompanying exemplarydrawings.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view, partially in section, depicting the stentembodying features of the present invention mounted on a deliverycatheter disposed within a vessel.

FIG. 2 is an elevational view, partially in section, similar to thatshown in FIG. 1, wherein the stent is expanded within a vessel, pressingthe lining against the vessel wall.

FIG. 3 is an elevational view, partially in section, showing theexpanded stent within the vessel after withdrawal of the deliverycatheter.

FIG. 4 is a plan view of one preferred embodiment of a flattened stentof the present invention, which illustrates the serpentine patternincluding peaks and valleys which form the cylindrical elements of thestent and permit the stent to achieve a small crimp profile, yet isexpandable to a larger diameter to maintain the patency of a smallvessel.

FIG. 5 is an enlarged partial view of the stent of FIG. 4 depicting theserpentine pattern along with the peaks and valleys which form onepreferred embodiment of a cylindrical element made in accordance withthe present invention.

FIG. 6 is a plan view of an alternative embodiment of a flattened stentof the present invention, which illustrates the serpentine pattern alongwith the peaks and valleys which form the cylindrical elements of thestent and permit the stent to achieve a small crimp profile, yet isexpandable to a larger diameter to maintain the patency of a smallvessel.

FIG. 7 is an enlarged partial view of the stent of FIG. 6 depicting theserpentine pattern along with the peaks and valleys which form anotherpreferred embodiment of a cylindrical element made in accordance withthe present invention.

FIG. 8 is a plan view of an alternative embodiment of a flattened stentof the present invention, which illustrates the serpentine pattern alongwith the peaks and valleys which form the cylindrical elements of thestent and permit the stent to achieve a small crimp profile, yet isexpandable to a larger diameter to maintain the patency of a smallvessel.

FIG. 9 is an enlarged partial view of the stent of FIG. 8 depicting theserpentine pattern along with the peaks and valleys which form anotherpreferred embodiment of a cylindrical element made in accordance withthe present invention.

FIG. 10 is a plan view of an alternative embodiment of a flattened stentof the present invention, which illustrates the serpentine pattern alongwith the peaks and valleys which form the cylindrical elements of thestent and permit the stent to achieve a small crimp profile, yet isexpandable to a larger diameter to maintain the patency of a smallvessel.

FIG. 11 is an enlarged partial view of the stent of FIG. 10 depictingthe serpentine pattern along with the peaks and valleys which formanother preferred embodiment of a cylindrical element made in accordancewith the present invention.

FIG. 12 is an enlarged view of a double-curved portion (w) which has asweep cut which helps the stent to be crimped to a low diameter.

FIG. 13 is a plan view of an alternative hybrid stent design inaccordance with the present invention.

FIG. 14 is a partial plan view of an alternative hybrid stent design inaccordance with the present invention.

FIGS. 15 a and 15 b is a plan view of an alternative hybrid stent designin accordance with the present invention illustrating the unit cells.

FIG. 16 is a plan view is a plan view of an alternative hybrid stentdesign in accordance with the present invention.

FIG. 17 is a plan view of an alternative hybrid stent design inaccordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Prior art stent designs, such as the MultiLink Stent™ manufactured byAdvanced Cardiovascular Systems, Inc., Santa Clara, Calif., include aplurality of cylindrical rings that are connected by three connectingmembers between adjacent cylindrical rings. Each of the cylindricalrings is formed of a repeating pattern of U-, Y-, and W-shaped members,typically having three repeating patterns forming each cylindricalelement or ring. A more detailed discussion of the configuration of theMultiLink Stent™ can be found in U.S. Pat. No. 5,569,295 (Lam) and U.S.Pat. No. 5,514,154 (Lau et al.), whose contents are hereby incorporatedby reference.

Beyond those prior art stents, FIG. 1 illustrates an exemplaryembodiment of stent 10 incorporating features of the present invention,which stent is mounted onto delivery catheter 11. FIG. 4 is a plan viewof this exemplary embodiment stent 10 with the structure flattened outinto two dimensions to facilitate explanation. Stent 10 generallycomprises a plurality of radially expandable cylindrical elements 12disposed generally coaxially and interconnected by interconnectingmembers 13 disposed between adjacent cylindrical elements 12. Thedelivery catheter 11 has an inner tubular member 14 upon which thecollapsed stent 10 is mounted. A restraining sheath 15 extends over boththe inner tubular member 14 and stent 10 in a co-axial relationship. Thestent delivery catheter 11 is used to position the stent 10 within anartery 16 or other vessel. The artery 16, as shown in FIG. 1, has adissected or detached lining 17 which has occluded a portion of thearterial passageway.

In a preferred embodiment, the delivery of the stent 10 is accomplishedin the following manner. Stent 10 is first mounted onto the deliverycatheter 11 with the restraining sheath placed over the collapsed stent.The catheter-stent assembly can be introduced within the patient'svasculature in a conventional Seldinger technique through a guidingcatheter (not shown). A guide wire 18 is disposed through the damagedarterial section with the detached or dissected lining 17. Thecatheter-stent assembly is then advanced over guide wire 18 withinartery 16 until the stent 10 is directly under the detached lining 17.The restraining sheath 15 is retracted exposing the stent 10 andallowing it to expand against the inside of artery 16, which isillustrated in FIG. 2. While not shown in the drawing, artery 16 ispreferably expanded slightly by the expansion of stent 10 to seat orotherwise embed stent 10 to prevent movement. Indeed, in somecircumstances during the treatment of stenotic portions of an artery,the artery may have to be expanded considerably in order to facilitatepassage of blood or other fluid there through.

While FIGS. 1-3 depict a vessel having detached lining 17, stent 10 canbe used for purposes other than repairing the lining. Those otherpurposes include, for example, supporting the vessel, reducing thelikelihood of restenosis, or assisting in the attachment of a vasculargraft (not shown) when repairing an aortic abdominal aneurysm.

In general, stent 10 serves to hold open the artery 16 after catheter 11is withdrawn, as illustrated in FIG. 3. Due to the formation of stent10, the undulating component of the cylindrical elements of stent 10 isrelatively flat in a transverse cross-section so that when stent 10 isexpanded, cylindrical elements 12 are pressed into the wall of artery 16and as a result do not interfere with the blood flow through artery 16.Cylindrical elements 12 of stent 10 that are pressed into the wall ofartery 16 will eventually be covered with endothelial cell growth thatfurther minimizes blood flow turbulence. The serpentine pattern ofcylindrical sections 12 provide good tacking characteristics to preventstent movement within the artery. Furthermore, the closely spacedcylindrical elements 12 at regular intervals provide uniform support forthe wall of artery 16, and consequently are well adapted to tack up andhold in place small flaps or dissections in the wall of artery 16 asillustrated in FIGS. 2 and 3.

The stresses involved during expansion from a low profile to an expandedprofile are generally evenly distributed among the various peaks andvalleys of stent 10. Referring now to FIGS. 4-5, one preferredembodiment of the present invention as depicted in FIGS. 1-3 is shownwherein each expanded cylindrical element 12 embodies a serpentinepattern having a plurality of peaks and valleys that aid in the evendistribution of expansion forces. In this exemplary embodiment,interconnecting members 13 serve to connect adjacent valleys of eachadjacent cylindrical element 12 as described above. The various peaksand valleys generally have U, W and inverted-U shapes, in a repeatingpattern to form each cylindrical element 12. It should be appreciatedthat the cylindrical element 12 can be formed in different shapeswithout departing from the spirit and scope of the present invention.

The cylindrical element 12 of this stent 10 includes double-curvedportions (W) 21 located in the region of the valley where eachinterconnecting member 13 is connected to an adjacent cylindricalelement 12. The peak portions (inverted-U) 22 and the valley portions(U) 23 also form the cylindrical element 12 of the stent 10. A shoulderregion 24 extending from each valley portion to peak portion (invertedU) 22 allows the peak portion to be nested in a tight formation next toan adjacent cylindrical element 12. This shoulder region 24 provides atransition region between the peak portions (inverted U) 22 and thevalley portions (U) 23 and double-curved portion (W) 21 to allowadjacent cylindrical elements to nest within one another and therebybetter support the artery walls with smaller gaps between stent struts.In this manner, the shoulder region 24 provides more dense coverage ofthe serpentine pattern of the cylindrical element to create a fairlyuniform strut pattern which fully supports the walls of the diseasedartery. For this reason, there are no or few areas of the stent wallwhich do not have struts for supporting the wall of the artery. Each ofthe valley portions (U) 23 forms a Y-shaped member when connected to aninterconnecting member 13. As can be seen in this particular design,each of the valley portions (W's and U's) 21 and 23 have aninterconnecting member which connects that cylindrical element 12 to anadjacent cylindrical element. As a result, each cylindrical element 12is connected to an adjacent cylindrical element by at least fourinterconnecting members 13. The peak portions (inverted “U”) 22 are notdirectly connected to any adjacent cylindrical element to allow forradial expansion. The eight interconnecting members 13 which areconnected to each cylindrical element 12 are discontinuous with eachother to produce a highly flexible stent that does not kink uponbending. This particular design allows the stent 10 to be placed intortuous anatomy, where the stent 10 will conform to the particularanatomy of the patient. For example, if the stent 10 is placed in acurved portion of a artery, then the flexibility of the stent will allowit to take on the same curved shape without kinking and will still becapable of fully supporting the artery. Additionally, the stent'sresistance to kinking helps prevent occlusion of the vessel lumen by thestent struts. Even though the stent 10 is flexible, it is still rigidwhen collapsed so that it can be placed on the delivery catheter andmoved into the desired location in the patient's vasculature.

The stent 10 also includes end rings 25 and 26 which comprise all “W”shaped portions 27 to provide additional strength to the ends of thestent 10. This “W” pattern also helps to increase the overallradiopacity of the stent by virtue of the additional material needed tocreate such a “W” pattern. As a result, the stent 10 should be easilyobservable by a physician using imaging instrumentation, such as afluoroscope.

In another embodiment of the present invention, as is shown in FIGS. 6and 7, the stent 10 made with six crowns or peak portions (inverted U)22, rather than the eight crowns shown in the previous embodiment.Otherwise, the strut pattern is virtually identical. The stent shown inFIGS. 6 and 7 include six valley portions, namely three valley portions(W) 21 and three valley portions (U) 23. This particular design also hassix discontinuous interconnecting members 13 which connect eachcylindrical element 12 to an adjacent cylindrical element. Again, theinterconnecting member 13 are connected to each of the valley portions(W) 21 and valley portion (U) 23 to help prevent shortening of the stentduring radio expansion. This pattern also helps increase the flexibilityof the strut. End rings 25 and 26 which comprise of all “W” shapedportions 27 provide additional strength to the ends of the stent 10,while increasing the radiopacity of the stent as well.

In another embodiment of the invention, as shown in FIGS. 8 and 9, thestent 30 is made with cylindrical elements 32 which include six crownsor peak portions (inverted U's) 29 and six valley portions, namely threevalley portions (W) 31 and three valley portions (U) 34. This particulardesign differs from the previous two embodiments by utilizing threecontinuous interconnecting members 33 which are utilized to connect eachof the cylindrical elements 32 to an adjacent cylindrical element. Eachinterconnecting member 33 is connected to the valley portion (W) 31which creates a continuous spine 35 which extends from one end 36 to theother end 37 of the stent 30. In this manner, the serpentine pattern ofeach individual cylindrical element 30 are in phase with each other inorder to help reduce the contraction of the stent along their lengthswhen expanded. These continuous spines 35 help prevent the stent 30 fromshortening when each of the cylindrical elements 30 are radiallyexpanded.

The cylindrical element 32 also differs from the previous embodimentssince a valley portion (U) 34 is not utilized to interconnect adjacentcylindrical elements to each other. However, the cylindrical element 32includes a shoulder region 38 which extends between each of the valleyportions and peak portions to provide a transition region which allowsthe peak portion (inverted U) 29 to be crimped in close proximity to anadjacent cylindrical element. In this manner, the stent 30 can becrimped down to a low profile which helps reduce the overall profile ofthe stent and delivery catheter when placing the stent 30 through thetortuous anatomy of the patient's vasculature.

In still another embodiment of the present invention, as is shown inFIGS. 10 and 11, a stent 40 is shown having a plurality of cylindricalelements 42 which are connected together by interconnecting members 43.Each of the cylindrical elements 42 include a peak portion (inverted U)39 and valley portions (W) 41 and valley portions (U) 44 which form thecomposite ring. In this particular design, five valley portions (W) 41are utilized and each of the cylindrical element 42 is connected to anadjacent cylindrical element 42 by an interconnecting member 43 which isconnected to the valley portion (W) 41. As with the previous embodiment,each interconnecting member 43 extends directly behind one another toform a continuous spine 45 which extends from one end 46 to the otherend 47 of the stent 40. In this particular embodiment, five continuousspines 45 are created on the composite stent 40. The peak portions(inverted U) 39 and the valley portion (U) 44 are not connected by anyinterconnecting members. The end ring 48 of this particular stent 40includes five double curved portions (W) 41 which helps increase theradial strength of this end while enhancing the radiopacity as well. Ascan be seen from the single cylindrical element 42 shown in FIG. 11, thedouble curved portion (W) 41 include a “sweep cut” 49 which helps toreduce the collapsed profile of the stent 40 when it is placed on adelivery catheter. This reduced portion of the double curved portion (W)21 enables the peak portion (inverted U) 39 to be collapsed closer tothe double curved portion (W) 41 without hitting the double-curvedportion (W) 41 when the stent 40 is crimped onto the delivery catheter.As a result, there should be no metal to metal contact when the stent iscrimped and the stent 40 should be crimped on to an even smaller profilewhich again helps in reducing the over profile of the stent and deliverycatheter and in reaching tight distal vessels. While this sweep cut 49is shown only in conjunction with the embodiment shown in FIGS. 10 and11, this sweep cut could be created on any of the other embodimentsdisclosed herein to help and reduce the overall diameter of the stentswhen they are being crimped on to the stent delivery catheters.

It should be appreciated that the present design can be made with anumber of peaks and valleys ranging from 4 to 16. The number of peaksand valleys will depend upon the particular physical characteristicsdesired, along with the particular application to which the stent willbe used.

In many of the drawing figures, the present invention stent is depictedflat, in a plan view for ease of illustration. All of the embodimentsdepicted herein are cylindrically-shaped stents that are generallyformed from tubing by laser cutting as described below.

One important feature of all of the embodiments of the present inventionis the capability of the stents to expand from a low-profile diameter toa larger diameter, while still maintaining structural integrity in theexpanded state and remaining highly flexible. Stents of the presentinvention each have an overall expansion ratio of about 1.0 up to about5.0 times the original diameter, or more, using certain compositions ofmaterials. The stents still retain structural integrity in the expandedstate and will serve to hold open the vessel in which they areimplanted. Some materials may afford higher or lower expansion ratioswithout sacrificing structural integrity.

While the stent design of the present invention has very practicalapplications for procedures involving vessel diameters from about 3.0 to14.0 millimeters, it should be appreciated that the stent pattern couldalso be successfully used in procedures involving larger lumens of thebody, without departure from the spirit and scope of the presentinvention. Due to the increase of the longitudinal flexibility providedby the present stent design, such applications could include largerdiameter vessels where added flexibility in reaching the vessel isneeded.

The stents of the present invention can be made in many ways. However,the preferred method of making the stent is to cut a thin-walled tubularmember, such as Nitinol tubing to remove portions of the tubing in thedesired pattern for the stent, leaving relatively untouched the portionsof the metallic tubing which are to form the stent. It is preferred tocut the tubing in the desired pattern by means of a machine-controlledlaser.

A suitable composition of Nitinol used in the manufacture of a selfexpanding stent of the present invention is approximately 55% nickel and44.5% titanium (by weight) with trace amounts of other elements makingup about 0.5% of the composition. The austenite transformationtemperature is between about −15.degree. C. and 30.degree. C. in orderto achieve superelasticity. The austenite temperature is measured by thebend and free recovery tangent method. The upper plateau strength isabout a minimum of 60,000 psi with an ultimate tensile strength of aminimum of about 155,000 psi. The permanent set (after applying 8%strain and unloading), is approximately 0.5%. The breaking elongation isa minimum of 10%. It should be appreciated that other compositions ofNitinol can be utilized, as can other self-expanding alloys, to obtainthe same features of a self-expanding stent made in accordance with thepresent invention.

The stent of the present invention can be laser cut from a tube ofsuper-elastic (sometimes called pseudo-elastic) nickel titanium(Nitinol) whose transformation temperature is below body temperature.All of the stent diameters can be cut with the same stent pattern, andthe stent is expanded and heat treated to be stable at the desired finaldiameter. The heat treatment also controls the transformationtemperature of the Nitinol such that the stent is super elastic at bodytemperature. The transformation temperature is at or below bodytemperature so that the stent will be superelastic at body temperature.The stent can be electro polished to obtain a smooth finish with a thinlayer of titanium oxide placed on the surface. The stent is usuallyimplanted into the target vessel which is smaller than the stentdiameter so that the stent applies a force to the vessel wall to keep itopen.

The stent tubing of a self expanding stent made in accordance with thepresent invention may be made of suitable biocompatible material besidessuper-elastic nickel-titanium (NiTi) alloys. In this case the stentwould be formed full size but deformed (e.g. compressed) to a smallerdiameter onto the balloon of the delivery catheter to facilitate intraluminal delivery to a desired intra luminal site. The stress induced bythe deformation transforms the stent from an austenite phase to amartensite phase, and upon release of the force when the stent reachesthe desired intra luminal location, allows the stent to expand due tothe transformation back to the more stable austenite phase. Furtherdetails of how NiTi super-elastic alloys operate can be found in U.S.Pat. No. 4,665,906 (Jervis) and U.S. Pat. No. 5,067,957 (Jervis).

The tubing also may be made of suitable biocompatible material such asstainless steel. The stainless steel tube may be alloy-type: 316L SS,Special Chemistry per ASTM F138-92 or ASTM F139-92 grade 2.

The stent diameters are very small, so the tubing from which it is mademust necessarily also have a small diameter. For PTCA applications,typically the stent has an outer diameter on the order of about 1 mm(0.04-0.09 inches) in the unexpanded condition, the same outer diameterof the hypotubing from which it is made, and can be expanded to an outerdiameter of 4.0 mm or more. The wall thickness of the tubing is about0.076-0.381 mm (0.003-0.015 inches). For stents implanted in other bodylumens, such as PTA applications, the dimensions of the tubing arecorrespondingly larger. While it is preferred that the stents be madefrom laser cut tubing, those skilled in the art will realize that thestent can be laser cut from a flat sheet and then rolled up in acylindrical configuration with the longitudinal edges welded to form acylindrical member.

Referring now to FIG. 5, the width of the strut of the cylindricalelement, indicated by arrows 50, can be about from 0.003 to 0.009inches. The width of the strut of the interconnecting member, indicatedby arrows 51, can be from about 0.003 to 0.009 inches. The length fromthe double-curved portion to the shoulder region, indicated by arrow 52,can be from about 0.05 to 0.10 inches. The length from the shoulderregion to the top of the peak portion, indicated by arrow 53, can befrom about 0.05 to 0.10 inches. The width of the peak portions(unexpanded) indicated by arrows 54, can be from about 0.012 to 0.040inches. These same dimensions would apply specifically to theembodiments of the present invention shown in FIGS. 6 and 7 and theembodiment of FIGS. 8 and 9.

Referring now to FIG. 12 the width of the strut of the cylindricalelement, indicated by arrows 50, can be about from 0.003 to 0.009inches. The width of the strut of the interconnecting member, indicatedby arrows 51, can be from about 0.003 to 0.009 inches. The length fromthe double-curved portion to the peak portion, indicated by arrow 52,can be from about 0.070 to 0.150 inches. The width of the peak portionsindicated by arrow 54, can be from about 0.03 to 0.06 inches.

Due to the thin wall and the small geometry of the stent pattern, it isnecessary to have very precise control of the laser, its power level,the focus spot size, and the precise positioning of the laser cuttingpath. In cutting the strut widths of the embodiment shown in FIGS. 1-5,it is preferable to have a very focused laser spot size which will allowthe precise strut pattern to be created on the tubing. For this reason,additional instrumentation which includes a series of lenses may benecessary to be utilized with the laser in order to create the finefocused laser spot necessary to cut that particular pattern.

Generally, the tubing is put in a rotatable collet fixture of amachine-controlled apparatus for positioning the tubing relative to alaser. According to machine-encoded instructions, the tubing is thenrotated and moved longitudinally relative to the laser which is alsomachine-controlled. The laser selectively removes the material from thetubing by ablation and a pattern is cut into the tube. The tube istherefore cut into the discrete pattern of the finished stent. Furtherdetails on how the tubing can be cut by a laser are found in U.S. Pat.No. 5,759,192 (Saunders) and U.S. Pat. No. 5,780,807 (Saunders), whichhave been assigned to Advanced Cardiovascular Systems, Inc. and areincorporated herein by reference in their entirety.

The process of cutting a pattern for the stent into the tubing generallyis automated except for loading and unloading the length of tubing. Forexample, a pattern can be cut in tubing using a CNC-opposing colletfixture for axial rotation of the length of tubing, in conjunction withCNC X/Y table to move the length of tubing axially relative to amachine-controlled laser as described. The entire space between colletscan be patterned using the CO.sub.2 or Nd:YAG laser set-up. The programfor control of the apparatus is dependent on the particularconfiguration used and the pattern to be ablated in the coding.

After the stent has been cut by the laser, electrical chemicalpolishing, using various techniques known in the art, should be employedin order to create the desired final polished finish for the stent. Theelectropolishing will also be able to take off protruding edges andrough surfaces which were created during the laser cutting procedure.

Referring now to FIGS. 13-16 there are shown alternative stent patterndesigns in accordance with an alternative embodiment of the presentinvention. For stenting in the carotid arteries it has been discoveredthat a specialized stent pattern is desired. More specifically it isdesirable to have a stent pattern design such that the ends of the stentare very flexible while the center portion of the stent is stiffer.Additionally, but having such a “hybrid” stent design, the scaffoldingpresented to the wall of the artery can be varied through patternchanges to address specific needs. A hybrid stent design can beperformed in many different manners, for example the pattern can beadjusted between “open cell” and “closed cell” patterns, adjusting thecell size between large and small, adjusting the cell geometry and strutdiameter. An example of such open cell and closed cell patterns isdisclosed in U.S. Pat. No. 5,827,321 (Roubin), the contents of which ishereby incorporated by reference in its entirety. Additionally, a hybridstent may be constructed of one or more materials.

Referring now to FIG. 13, there is shown a design for a hybrid stent inaccordance with the present invention. As shown in FIG. 13, the hybriddesign includes a plurality of transition zones along the length of thestent wherein the pattern changes from an open cell design to a closedcell design then back to an open cell design.

Referring to FIGS. 13 and 14 there is shown an exemplary embodiment of ahybrid stent in accordance with the present invention, wherein the stent100 is constructed of a plurality of radially expandable cylindricalelements 120 disposed generally coaxially and interconnected byinterconnection members 113. As shown in the figures and particularly inFIG. 14, the number of interconnection members 113 can be varied betweeneach of the adjacent radially expandable cylindrical elements 120 toform the various sections as labeled in FIG. 13. For example, for theopen sections (102), the number of interconnection members 113 disposedbetween the adjacent cylindrical elements 120 is far fewer than thenumber of interconnection members 113 in transition section 104 and inthe closed section 106. The closed section 106 includes aninterconnection member extending between each adjacent peak or valley ofthe adjacent cylindrical members 120. By varying the number ofinterconnection members 113 as shown in FIGS. 13 and 14 the flexibilityof the stent as well as the scaffolding ability of the stent can bevaried. If a hybrid stent was produced without the transition section104, the flexibility of the stent would not be linear along the lengthof the stent, instead there would be peaks in flexibility curve whichwould be undesirable.

Referring now to FIGS. 15 a and 15 b, there is shown an exemplaryembodiment of a prior art design and the unit cell thereof (darkenedportion) and an exemplary embodiment of the hybrid stent design inaccordance with the present invention. As shown in FIG. 15 a, the stentdesign shown therein includes a single unit cell which extends along thelength of the stent in a repeated pattern. By contrast, the hybrid stent100 of FIG. 15 b illustrates the four different unit cells thereof,illustrating the difference between the open cell and closed cell andtransition cell of the exemplary stent pattern.

Referring now to FIG. 16 there is shown yet another exemplary embodimentof a hybrid stent in accordance with the present invention. As shown inFIG. 16, the hybrid stent 200 includes a plurality of cell designs alonga length thereof, wherein only a portion of the stent has been shown forsimplicity. As shown, the stent includes an open cell portion, atransition section and a closed cell portion. The interconnectionmembers 213 maybe embodied in the form of linear elements extendingbetween adjacent cylindrical members 220 or may include a feature formedtherein as shown at 214. Further still, the interconnection members maybe disposed at an angle to an axis of the stent as shown by referencenumber 215. The feature formed in the interconnection members maybeformed to compensate for foreshortening or to aid in flexibility or totransition flexibility along the length of the stent.

Referring now to FIG. 17, there is shown yet another exemplaryembodiment of an alternative hybrid stent design in accordance with thepresent invention. As shown in FIG. 17, the hybrid stent shown thereinincludes a varying number of interconnection members adjacent to theends of the stent, whereby the pattern of the stent can be transitionedbetween an open cell design and a closed cell design.

It shall be understood that the cylindrical members shown in theembodiments herein are merely exemplary and that multiple types ofcylindrical members have been shown herein to illustrate the concepts ofthe present invention.

While the invention has been illustrated and described herein in termsof its use as intra vascular stents, it will be apparent to thoseskilled in the art that the stents can be used in other instances in allconduits in the body, such as, but not limited to, the urethra andesophagus. Other modifications and improvements may be made withoutdeparting from the scope of the invention.

The invention claimed is:
 1. A delivery system comprising: a deliverycatheter having a proximal end and a distal end; and a stent disposed atthe distal end of the delivery catheter, the stent including: aplurality of radially expandable rings disposed adjacent to one anotherto define a tubular member having a proximal end portion, and a distalend portion, and a middle portion, each of the radially expandable ringsincluding a plurality of strut members; at least one interconnectionmember disposed between a first expandable ring and a second radiallyexpandable ring and extending between strut members thereof at an endportion of the tubular member to define an open cell bordered by the atleast one interconnection member and three or more struts of the firstexpandable ring and of the second radially expandable ring,respectively; a plurality of interconnection members included in themiddle portion of the tubular member and extending betweenlongitudinally adjacent expandable rings, the number of the plurality ofthe interconnection members in the middle portion of the tubular memberbeing greater than that of the end portion of the tubular member, andwherein a transition section is defined between the end portion and themiddle portion, the transition section including at least one open celldefined between at least two longitudinally adjacent expandable rings ofthe transition section and at least one closed cell defined between theat least two longitudinally adjacent expandable rings, each open cellbordered by circumferentially adjacent interconnection members extendingbetween two longitudinally adjacent expandable rings of the transitionsection and by three or more struts of each of the two longitudinallyadjacent expandable rings, respectively, and each closed cell borderedby circumferentially adjacent interconnection members extending betweenthe two longitudinally adjacent expandable rings and by two struts ofeach of the two longitudinally adjacent expandable rings.
 2. Thedelivery system of claim 1, wherein the middle portion of tubular memberof the stent comprises the plurality of interconnection members disposedbetween longitudinally adjacent radially expandable rings to defineclosed cells therebetween, each closed cell bordered bycircumferentially adjacent interconnection members and by two struts ofeach of the longitudinally adjacent rings of the middle portion.
 3. Thedelivery system of claim 1, wherein the at least one closed cell and theat least one open cell of the transition section of the tubular memberof the stent are disposed circumferentially adjacent to each other. 4.The delivery system of claim 1, wherein at least one of the plurality ofradially expandable rings of the stent includes a W shaped portion at alocation adjacent to the at least one interconnection member.
 5. Thedelivery system of claim 1, wherein at least two adjacent expandablerings of the plurality of radially expandable rings include a W shapedportion and a U shaped portion.
 6. The delivery system of claim 1,wherein at least one of the distal expandable ring and the proximalexpandable ring of the stent includes strut members defining a W shapedportion.
 7. The delivery system of claim 1, wherein the at least one ofthe plurality of radially expandable rings of the stent includes a Wshaped portion defined by strut members, an inverted U shaped portiondefined by strut members, and a U shaped portion defined by strutmembers.
 8. The delivery system of claim 7, wherein at least one of theplurality of radially expandable rings of the stent includes alternatingW shaped portions and U shaped portions along at least a portion of thelength of the ring.
 9. The delivery system of claim 1, wherein aplurality of interconnection members of the stent are configured to forma continuous spine which extends from the proximal end to the distal endof the stent.
 10. The delivery system of claim 1, wherein at least oneof the plurality of radially expandable rings of the stent includes atleast one shoulder region extending from a valley portion to a peakportion.
 11. The delivery system of claim 10, wherein the peak portionis expandable.
 12. The delivery system of claim 11, wherein the numberof interconnection members between each of the longitudinally adjacentexpandable rings differ from each other.
 13. The delivery system ofclaim 1, wherein the at least one interconnection member includes anon-linear portion.
 14. The delivery system of claim 1, wherein thestent is self-expandable.
 15. The delivery system of claim 14, whereinthe stent is made from Nitinol.
 16. The delivery system of claim 1,wherein the stent is balloon-expandable.
 17. The delivery system ofclaim 1, wherein the delivery catheter includes an inner tubular memberupon which the stent is mounted.
 18. The delivery system of claim 1,wherein the delivery catheter includes a retractable sheath.
 19. Thedelivery system of claim 18, wherein the delivery catheter includes aninner tubular member upon which the stent is mounted , and wherein theretractable sheath extends over the stent.
 20. The delivery system ofclaim 1, wherein the delivery catheter includes a balloon upon with thestent is mounted.